Silica, alumina and their amorphous mixtures are well known as catalysts used in hydrocarbon conversion process. The method of preparation clearly controls the resultant activity (such as cracking or isomerization activity), and physical properties (such as pore structure and volume, surface area, density and catalyst strength). Silica/alumina catalysts such as in the present invention can be used "as is", particularly in reactions that require acidic catalysts, or can optionally be combined with zeolites, clays or other binders, and inorganic oxides for the cracking of liquid hydrocarbons in cracking reactors such as fluid catalytic crackers.